Windows Defender must be manually enabled. To enable Windows Defender, open the Windows Action Center and enable Windows Defender.
How to enable Windows Defender for Windows 7:
- Click Start
- Click Control Panel > System and Security > Action Center
- Next to Windows Defender is turned off, click Turn on now
- Close the Action Center window
How to enable Windows Defender for Windows 8:
- Click Start (or press the Start button on the keyboard)
- Type the following: Action Center
- Click Settings (top-right of screen)
- Click Action Center (left of screen)
- Next to Windows Defender is turned off, click Turn on now
- Close the Action Center window